A great many water soluble dyes which contain sulfonic acid substitutes have been made over the past century. Such dyes have traditionally found application as acid dyes for woolen fabric materials. With the development of nylon, certain of the acid dyes have been used as colorants for nylon fiber. Although extensive research has been conducted in this area of dye chemistry, recent demands for dyes with specific properties applicable to new fabric materials has rendered many of the earlier dyes inadequate for modern needs.
One example of a specialized area of dye application is carpet dyeing, and particularly, nylon carpet dyeing. In the dyeing of carpets it is necessary to provide a dye with excellent "transfer" properties, i.e., the ability to produce level dyeings even in heavy carpets and with filaments of a large diameter. In the dyeing of nylon carpeting other problems occur which are caused by variations in the carpeting itself. For example, nylon carpeting may have localized areas of differing crystallinity, due perhaps to differing stresses established in the cold drawing to which the fiber is subjected during manufacture. Such localized areas accept acid dyes at different rates and in varying amounts, depending upon the physical characteristics of the carpet in each area. With a dye of excellent transfer properties, it is possible to dye such carpeting with an evenness not possible with dyes lacking these properties. In addition to transfer properties, fastness to light is also an important consideration.
The need for finding dyes capable of adequately dyeing nylon carpeting is emphasized by the fact that nylon is the most important fiber used in the United States for carpeting. It has been reported that, in 1972, 925 million pounds of nylon was used in carpeting, an amount representing 65.6% of all fibers used in U.S. carpet manufacture. It is estimated that this amount will increase to 1714 million pounds by 1978.
Available nylon carpet fiber is generally classified as to type, depending upon its receptivity to acid dyes and basic or cationic dyes. Cationic dyeable nylon contain SO.sub.3 H groups or COOH groups which are receptive to cationic or basic dyes. Acid dyeable nylons are essentially conventional nylons, such as polyhexamethylene adipamide and polycaprolactam. Acid dyeable nylons vary as to type and are characterized as being weakly dyed with acid dyes, average dyed with acid dyes, or deeply dyed with acid dyes. DuPont Technical Information Bulletin N-260, September, 1972, describes the types of commercially available nylon fibers.
Deep dyeing acid dyeable nylon disadvantageously changes many conventional acid dyes to red and dull shades in moderate to heavy dyeings. By moderate to heavy shades is meant dyeing of about 0.5% owf to about 4% owf.
Tufted or woven carpet material comprising mixtures of the above yarn types will yield attractive multicolored carpet when dyed with appropriate dyes. For example a carpet tufted or woven with a cationic dyeable nylon and an acid dyeable nylon can be dyed with two colors such as yellow and red by dyeing the cationic dyeable portion with a red cationic or basic dye and the acid dyeable portion with a yellow acid dye. The dyeing operation is usually done in one application; that is, both the cationic and acid dye are applied to the carpet in one dyebath or in one application step.
It is essential in the production of multicolor carpets made from styling yarns that the acid dyes used to dye the acid dyeable portion of the carpet do not dye or stain the cationic dyeable portions. Useful acid dyes besides requiring outstanding light fastness and good transfer and leveling properties should dye only the acid dyeable nylon because, in spite of the fact that a minor degree of staining of the cationic dyeable portion can be tolerated, the value of an acid dye for application to carpet containing cationic dyeable nylon is considerably enhanced if, upon application of the dye, the cationic dyeable portion remains substantially unstained. The reason for this is that unstained or very lightly stained cationic or basic dyeable nylon will be brighter when it is dyed with a basic dye. Conversely, as the amount of staining increases, the dyed basic portion will become dull in appearance.
The acid dye, in addition to the above requirements, also should not change shade when dyed in moderate to heavy shades on the acid dyeable nylon. Conventional dyes recommended for acid dyeable nylon of the same shade as dyes of this invention, as stated above, are characterized by the undesirable property of becoming red and dull in heavy dyeings, especially on deep dyeing acid dyeable nylon, such as, for example, DuPont T-847 acid dyeable nylon yarn.
It has now been discovered, according to the present invention, that a small class of monoazo acid dyes possess superior dyeing properties. These dyes are characterized by outstanding lightfastness and outstanding leveling and transfer properties. The dyes are also characterized by low stain on cationic dyeable nylon and by the absence of the property of changing shade to red and dull shades in heavy dyeings, especially on deep dyeing nylon yarn. The class of dyes according to the present invention includes previously unreported dyes and also those of known structure such as C.I. 13150 (C.I. Acid Orange 50). This latter dye was discovered in 1935 and was first used as a wool color.